1. Field of the Invention
The present invention relates to a tool and a method for measuring depths of countersunk holes and, in particular, a tool having simple structure and a method that is correspondingly quick and accurate.
2. Description of Related Art
China Patent Application No. 95194539.4 discloses a method for measuring depths of holes that utilizes reflection or transmission of light. Maximum and minimum light intensities vary according to the depths of the holes being measured. Then by comparing a structure and its corresponding light wavelength, a depth of a hole can be determined. However, the method is only for measuring the depth of a cylindrical hole. Numerous structures have holes comprising a countersunk portion adjoining a cylindrical portion. Typically, the countersunk portion is tapered such that it resembles a truncated cone. The disclosed method cannot accurately measure depths of such holes.
Accordingly, an object of the present invention is to provide a tool having simple structure and low cost for measuring depths of countersunk holes accurately and quickly.
Another object of the present invention is to provide a method for measuring a depth of a countersunk hole accurately and quickly.
To achieve the first above-mentioned object, a tool of the present invention for measuring depths of countersunk holes includes a worktable, a measuring member and a display device. The worktable comprises a measuring plate defining four adjusting screw holes in four comers thereof, and four adjusting rods adjustably attached in the adjusting screw holes below the measuring plate. The extents to which the adjusting rods are received in the adjusting screw holes are adjusted so that the measuring plate can be level. The measuring member is generally cylindrical, and comprises a cylindrical head having a conical tip. The display device comprises a vertical central shaft, and a bearing sleeve surrounding a bottom of the central shaft. The central shaft can move vertically through the bearing sleeve. The display device further comprises a cylindrical body having a display showing a height value of a top face of the central shaft, and a zeroing button.
A typical workpiece defines a tapered countersunk hole, and a cylindrical hole below and in communication with the countersunk hole. An angle of inclination of the conical tip of the measuring member is less than a corresponding angle of inclination of an inner inclined annular wall of the workpiece at the countersunk hole.
When measuring a depth of the countersunk hole of the workpiece, the cylindrical hole of the workpiece is placed around the conical tip of the measuring member. The workpiece is pressed downwardly so that a bottom face thereof abuts the measuring plate. The zeroing button is pressed, and zero is shown on the display of the display device. Then the workpiece is turned upside down, and the countersunk hole is placed around the conical tip of the measuring member. The workpiece is pressed downwardly so that an inverted top face thereof abuts the measuring plate. The value shown on the display is equal to the depth of the countersunk hole.